<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        * {
            box-sizing: border-box;
        }
        .outBox {
            position: fixed;
            top: 0;
            bottom: 0;
            left: 0;
            right: 0;
            background: rgba(100, 100, 100, 0.5);
        }

        .inBox {
            width: 500px;
            margin:0 auto;
            margin-top:10% ;
            background: rgba(0, 100, 100, 0.5);
        }
    </style>
</head>
<body>
<div class="outBox">
    <div class="inBox">
        Lorem ipsum dolor sit amet, consectetur adipisicing elit. Consequuntur deserunt dolor dolorem doloremque
        fugiat illum inventore magnam maxime necessitatibus pariatur placeat provident quam quia quibusdam quidem
        sapiente sint, tempora, voluptates!
        hahahahhahahahahah
    </div>
</div>
<script>

</script>
</body>
</html>